[Qemu-devel] [PATCH 10/18] vhost-user: add slave-fd support

[marcandre.lureau@redhat.com]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

Learn to give a socket to the slave to let him make requests to the
master.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 docs/specs/vhost-user.txt | 23 ++++++++++++++++
 hw/virtio/vhost-user.c    | 69 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+)

diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
index 0312d40..8a635fa 100644
--- a/docs/specs/vhost-user.txt
+++ b/docs/specs/vhost-user.txt
@@ -248,12 +248,25 @@ Once the source has finished migration, rings will be stopped by
 the source. No further update must be done before rings are
 restarted.
 
+Slave communication
+-------------------
+
+An optional communication channel is provided if the slave
+declares VHOST_USER_PROTOCOL_F_SLAVE_CHANNEL feature, to allow
+the slave to make requests to the master.
+
+The fd is provided via VHOST_USER_SET_SLAVE_FD ancillary data.
+
+A slave may then send VHOST_USER_SLAVE_* messages to the master
+using this fd communication channel.
+
 Protocol features
 -----------------
 
 #define VHOST_USER_PROTOCOL_F_MQ             0
 #define VHOST_USER_PROTOCOL_F_LOG_SHMFD      1
 #define VHOST_USER_PROTOCOL_F_RARP           2
+#define VHOST_USER_PROTOCOL_F_SLAVE_CHANNEL  3
 
 Message types
 -------------
@@ -464,3 +477,13 @@ Message types
       is present in VHOST_USER_GET_PROTOCOL_FEATURES.
       The first 6 bytes of the payload contain the mac address of the guest to
       allow the vhost user backend to construct and broadcast the fake RARP.
+
+ * VHOST_USER_SET_SLAVE_FD
+      Id: 20
+      Equivalent ioctl: N/A
+      Master payload: N/A
+
+      Set the file descriptor for the salve to make VHOST_USER_SLAVE_*
+      request to the master. It is passed in the ancillary data.
+      This message is only sent if VHOST_USER_PROTOCOL_F_SLAVE_CHANNEL
+      feature is available.
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 02ac1fc..890c1bd 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -32,6 +32,7 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_MQ = 0,
     VHOST_USER_PROTOCOL_F_LOG_SHMFD = 1,
     VHOST_USER_PROTOCOL_F_RARP = 2,
+    VHOST_USER_PROTOCOL_F_SLAVE_CHANNEL = 3,
 
     VHOST_USER_PROTOCOL_F_MAX
 };
@@ -59,9 +60,16 @@ typedef enum VhostUserRequest {
     VHOST_USER_GET_QUEUE_NUM = 17,
     VHOST_USER_SET_VRING_ENABLE = 18,
     VHOST_USER_SEND_RARP = 19,
+    VHOST_USER_SET_SLAVE_FD = 20,
+
     VHOST_USER_MAX
 } VhostUserRequest;
 
+typedef enum VhostUserSlaveRequest {
+    VHOST_USER_SLAVE_NONE = 0,
+    VHOST_USER_SLAVE_MAX
+}  VhostUserSlaveRequest;
+
 typedef struct VhostUserMemoryRegion {
     uint64_t guest_phys_addr;
     uint64_t memory_size;
@@ -110,6 +118,7 @@ static VhostUserMsg m __attribute__ ((unused));
 
 struct vhost_user {
     CharDriverState *chr;
+    int slave_fd;
 };
 
 static bool ioeventfd_enabled(void)
@@ -513,6 +522,55 @@ static int vhost_user_reset_device(struct vhost_dev *dev)
     return 0;
 }
 
+static void slave_read(void *opaque)
+{
+    struct vhost_dev *dev = opaque;
+    struct vhost_user *u = dev->opaque;
+    VhostUserMsg msg = { 0, };
+    int size;
+
+    size = read(u->slave_fd, &msg, VHOST_USER_HDR_SIZE);
+    if (size != VHOST_USER_HDR_SIZE) {
+        error_report("Failed to read from slave.");
+        qemu_set_fd_handler(u->slave_fd, NULL, NULL, NULL);
+        close(u->slave_fd);
+        u->slave_fd = -1;
+        return;
+    }
+
+    switch (msg.request) {
+    default:
+        error_report("Received unexpected msg type.");
+    }
+}
+
+static int vhost_setup_slave_channel(struct vhost_dev *dev)
+{
+    VhostUserMsg msg = {
+        .request = VHOST_USER_SET_SLAVE_FD,
+        .flags = VHOST_USER_VERSION,
+    };
+    struct vhost_user *u = dev->opaque;
+    int sv[2];
+
+    if (!virtio_has_feature(dev->protocol_features,
+                            VHOST_USER_PROTOCOL_F_SLAVE_CHANNEL)) {
+        return 0;
+    }
+
+    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
+        error_report("socketpair() failed");
+        return -1;
+    }
+
+    u->slave_fd = sv[0];
+    qemu_set_fd_handler(u->slave_fd, slave_read, NULL, dev);
+
+    vhost_user_write(dev, &msg, &sv[1], 1);
+
+    return 0;
+}
+
 static int vhost_user_init(struct vhost_dev *dev, void *opaque)
 {
     uint64_t features;
@@ -523,6 +581,7 @@ static int vhost_user_init(struct vhost_dev *dev, void *opaque)
 
     u = g_new0(struct vhost_user, 1);
     u->chr = opaque;
+    u->slave_fd = -1;
     dev->opaque = u;
 
     err = vhost_user_get_features(dev, &features);
@@ -563,6 +622,12 @@ static int vhost_user_init(struct vhost_dev *dev, void *opaque)
                    "VHOST_USER_PROTOCOL_F_LOG_SHMFD feature.");
     }
 
+
+    err = vhost_setup_slave_channel(dev);
+    if (err < 0) {
+        return err;
+    }
+
     return 0;
 }
 
@@ -573,6 +638,10 @@ static int vhost_user_cleanup(struct vhost_dev *dev)
     assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
 
     u = dev->opaque;
+    if (u->slave_fd >= 0) {
+        close(u->slave_fd);
+        u->slave_fd = -1;
+    }
     g_free(u);
     dev->opaque = 0;
 
-- 
2.5.5